All MacBook Pros that I've seen (I have 2, employees have them, many friends, colleagues, and clients have them) have 3 prong connectors. Never once had a buzz from any of them.

I think it's more to do with the specific power supply or laptop and not just the 'presence of a 3-prong adapter'.

Question though, I've seen many PC's without a ground prong on their adapter. Are these inherently unsafe, or is there something different about those power supplies? In other words, why is it unsafe to remove the ground prong from a 3-prong supply when some PC's only come with a 2-prong supply in the first place?

I've had several laptop noise problems that were cleared up by simply running them on the internal battery power. One computer with a "short life" weak internal battery had the problem solved by using a 12V alarm system back-up battery wired to the computer's automotive power supply cable in an "emergency".

Question though, I've seen many PC's without a ground prong on their adapter. Are these inherently unsafe, or is there something different about those power supplies? In other words, why is it unsafe to remove the ground prong from a 3-prong supply when some PC's only come with a 2-prong supply in the first place?

If there is no ground pin, then the deice being powered must be designed and built to make it incapable of giving someone a shock. This is most commonly done by making the thing "double insulated", which has the two square boxes symbol.

The other approach is to ground stuff, so if a fault occurs, then then effectively the fault current is shorted to ground causing a fuse to pop. So, if you chop off the ground pin, there is no safe return path, and under fault conditions, someone can become shocked.